Mississippi Crop Situation

Management Guidelines for Sugarcane Aphids in MS Grain Sorghum 2015

By Angus Catchot, Extension Entomologist, Jeff Gore, Research and Extension Entomologist and Don Cook, Research Entomologist
February 24, 2015 16:42

In 2014 a new pest of MS grain sorghum, Sugarcane aphid, made a dramatic entry infesting every county that grew the crop. This pest originally showed up in grain sorghum in Texas and Louisiana in 2013 with a single find very late in the season in Bolivar County, MS. By the end of 2014, this pest quickly spread throughout the entire southeast. The pest proved to be very devastating in the absence of timely control. Current estimates for MS is that approximately 70% of the acres were treated at least once and losses averaged about 15% for the state. Through collaboration with LSU AgCenter and Texas A&M we were quickly able to implement some of their experiences from the prior year. Since that time and numerous trials in 2014, we have been able to refine our recommendations for MS for the current crop year. At times last year many wondered if this pest would be the death of grain sorghum in our state, myself included. After a solid year of research and testing behind us, with the addition of more products available, I am confident we can deal with this pest and grow grain sorghum successfully but we need plan for it.

PLANNING FOR 2015:

The following are discussed throughout:

1) Plant early – Most of the early planted milo did not experience high levels of sugarcane aphids last year. We do not know if they avoided them because the aphid was not fully established in MS yet or if this method will be a true cultural control method like in other crops but it is a good recommendation regardless.

2) Higher plant populations and/or narrow rows – this is only anecdotal but we observed much lower infestations where plantings were thick or rank whether this was from twin rows, narrow rows, or simply more seed per acre. Warning: this is not proven but held up on numerous operations. Aphids seem to like thin and skippy stands much more. May want to stay on the high end of seeding recommendations.

3) Use insecticide seed treatment- this is a must to avoid early season infestations requiring additional foliar sprays

4) Avoid all disruptive sprays unless ABSOLUTELY necessary

5) Use tips and GPA to maximize coverage to the bottom of the canopy

6) Scout 2X per week when the first aphids are found

7) Watch for late season head colonization

DAMAGE AND YIELD LOSS POTENTIAL

As we moved into the 2014 growing season we quickly learned that this aphid had the potential to cause substantial yield loss if left untreated or if timely applications were not made to control it. Once aphids are first detected at very low levels, we observed populations to linger sometimes for 14-21 days increasing slowly. Once populations reached about 20-30% infestation level, populations expanded exponentially infesting nearly every plant in the field or substantial portions of the field within 5-10 days (closer to 5 days if a pyrethroid was added and killed beneficials). This is the point where control was absolutely essential to avoid catastrophic yield loss. Another observation from 2014 was that insecticide seed treatments of thiamethoxam or clothianidan held infestations off about 30-40 days. Seed treatments then began to fall off and populations began to increase. The pre-boot stage infestations also appear to be potentially more damaging. We witnessed many fields where infestations started during the pre-boot or boot stage and when not controlled the sorghum did not head out resulting in complete loss. The table below summarizes our data from 2014 yield trials where infestations originated at different growth stages. Keep in mind these data were generated from limited trials in MS in 2014 and as we do more testing these numbers can and will likely change.

You can see from the table that potential yield loss from sugarcane aphids extremely high if populations are allowed to go untreated. Surprisingly, we still saw yield loss as high as 21% when infestations originated as late as the soft dough stage.

THRESHOLDS AND CONTROL

Scouting for sugarcane aphids in grain sorghum has not proven to be difficult. We can quickly determine presence or absence by simply taking a sweep net handle and lifting lower leaves and examining undersides very quickly. This has proven to be my preferred method of initial detection. This aphid appears to be a prolific honeydew producer compared to other aphid species. Often you can simply scout for shiny honeydew on the leaves after the canopy drys from overnight dew to quickly detect presence or absence. This is important because once aphids are found IT IS CRITICAL to scout fields twice per week to monitor infestations because they expand rapidly. Some states are using aphid counts as thresholds where they recommend treating when infestations reach a certain percent level with at least 250 aphids per leaf. We have found that by adding the caveat of “localized heavy honeydew and established aphid colonies” to our percentage, you will always be at the right number of aphids per leaf for treatment when you hit the 20 or 30% infested plants because this generally refers to areas with thousands of aphids. This seems to resonate well with our consultants. The table below is a revised version of what put out last year based on our experience from 2014. Example: Depending on growth stage, when 20-30 plants out of 100 have aphids and you can find areas of the field where honeydew is heavy with numerous aphids, treatment is suggested.

TREATMENT AND EXPECTATIONS

We tested numerous compounds last year for control of sugarcane aphids. In short very little worked with exception of Transform, which we had received a section 18 emergency exemption. We have submitted again for this exemption with the EPA and are awaiting word back from them (Approved on 3/1/15). We have also submitted a Section 18 for Centric. Since that time Bayer CropScience received a full section 3 label for a new product called Sivanto. It is registered and there is a 2ee label allowing use rates of 4-7 oz/acre. No concrete word on cost yet but rumors are that it will be comparable to Transform. For Mississippi we will not be recommending the use of Dimethoate or Lorsban at all. Our testing suggested extremely erratic control with either of these products and in some cases actual flaring once beneficials were killed.

Because there appears to be no epizootic fungus that will keep numbers in check like we see with cotton aphids, the only natural help we get is from beneficial insects such as lady beetles. Often times beneficial numbers alone are not enough to avoid a spray but they certainly reduce the speed of growth of the population. This is very evident when we see a disruptive spray go out that eliminates the predators. We witnessed this many times with fall armyworm and midge sprays with pyrethroid insecticides this past year.

On average in 2014 we saw 10-14 days control with Transform. It is critical that we do whatever we can to increase coverage. Five gallons by air is an absolute minimum and we would prefer more. By ground 15-20 GPA is preferred.

HARVEST PROBLEMS

Although the likelihood of direct yield loss is slight once hard dough stage is reached, however, this aphid has been know to move into the head where it deposits large amounts of honeydew. Honeydew is like syrup, sticky and messy. There are numerous reports out of TX and LA of combine throats being stopped up from sticky residue trying to feed through. Watch for this closely after the crop reaches black layer. If you see aphids colonizing in the head, you may require a late application but you must be careful about the pre-harvest intervals on the label. Transform is 14 days and Sivanto is 21. The following pictures show aphids moving up stem to head and head colonization.

INSECTICIDE BUDGET

I would budget the following for insecticide usage in grain sorghum in MS and don’t forget to budget application cost. You may not need all of these applications, especially if you avoid automatic midge sprays that most certainly will make the aphid problem worse.

I would like to reiterate that grain sorghum is a very important crop in our mix that provides fantastic rotational benefits for weed control and nematode. Although it is important to understand the threat from this pest, it is equally important to understand that we can manage this pest but we have to stay on top of it. We are very worried about resistance development with Transform and it will be critical to rotate in Sivanto and hopefully Centric this year (pending exemption). At this time chemical rotation of different Modes of Action appears to be the only resistance management tool we have until breeders develop commercially resistant germplasm.

By Angus Catchot, Extension Entomologist, Jeff Gore, Research and Extension Entomologist and Don Cook, Research Entomologist
February 24, 2015 16:42

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